For psychopaths, empathy is a switch they can choose whether to turn on or off.

This is the conclusion a group of Dutch researchers came to after examining the brain activity of 18 psychopaths jailed for criminal acts, and a control group -- both of whom were shown videos of one person hurting another.

While the control group immediately reacted with a wave of activity, the psychopathic individuals only did so when asked.

This, the authors of the research believe, explains why psychopaths are capable of being seemingly so charming and so cruel. Furthermore, they argue that the stereotype of a completely unfeeling character is inaccurate, seeing as their brains did react when asked. The only difference is that they can turn it off.

Published in the journal Brain, the study consisted of three parts.

In the first stage of the experiment, all participants watched short movie clips of two people interacting with each other zoomed in on their hands. During the clip the hands touched in a loving, painful, socially rejecting and neutral manner. The only instructions given were to watched the movie the same way they would their favorite film, first author of the paper and graduate student at the University of Groningen Harma Meffert said.

Next, the participants watched the clips again. This time, however, the researchers told them explicitly to "empathize with one of the actors in the movie."

Finally, the researchers performed similar hand interactions with the participants themselves while their brain was scanned.

"We wanted to know to what extent they would activate the same brain regions while they were watching the hand interactions in the movies, as they would when they were experiencing these same hand interactions themselves," Meffert explained.

The human brain is equipped with something scientists call a "mirror system," which responds to others' actions or experiences by activating regions in their own brain that correspond to the other person's experience.

This phenomenon, many believe, likely constitutes a crucial part of someone's ability to feel empathy with previous studies demonstrating that the less this system is activated, the less a person reports empathizing with other people.

And while it has been suggested that individuals with psychopathy might somehow suffer from a broken mirror system, Meffert and her colleagues' study suggests a more complex picture, they argue.

Instead of generally activating their mirror system less, individuals with psychopathy appear to simply not engage in the behavior spontaneously.

"When explicitly asked to empathize, the differences between how strongly the individuals with and without psychopathy activate their own actions, sensations and emotions almost entirely disappeared in their empathic brain," explained Valeria Gazzola, the second author of the paper.

For this reason, she concluded that rather than an inability to empathize, psychopathy is characterized by "a reduced propensity to empathize, paired with a preserved capacity to empathize when required to do so."